1. Field of the Invention
The present invention is directed to a distance sensor for providing an electrical signal identifying a spacing between two components, and in particular to a distance sensor suitable for use in a computed tomography apparatus for measuring the distance between two components which are moved relative to one another.
2. Description of the Prior Art
A problem exists in the design and operation of computed tomography systems to maintain a precise positioning of the rotational center of the rotating scan frame, the scan frame rotating inside a stationary (non-rotating) gantry. The scan frame rotates inside the gantry with a clearance or spacing between the gantry and the scan frame, and one way to monitor the position of the rotational center is to identify any changes in the spacing between the rotating scan frame and the stationary gantry.
German Patentschrift 12 15 384 discloses an arrangement for non-contacting measurement of the axial displacement of a shaft relative to a fixed point. In this known arrangement, a measuring mark, which influences the path of a measuring radiation (light) ray, is attached to the shaft. The measuring mark has a geometrical shape which is designed so that the duration of a signal which is generated while the mark is influencing the path of the measuring ray is dependent on the amount of displacement of the shaft. This arrangement, however, is not suitable for determining migration of the rotational center of a computed tomography apparatus from a specified position, because such migration takes place in a radial direction.